As a rapid spread in the market of small-size or portable electronic devices such as note-type personal computers and portable telephone devices has appeared in recent years, the requirements for reducing the weight and increasing the capacity of the battery to be used therefor have been on the increase. In order to respond to these requirements, a development has been aggressive of the secondary battery which utilizes an electrochemical reaction through delivery and receipt of charges by charge carriers of alkali metal ions such as lithium ions. The lithium ion secondary battery with a large density and high capacity battery as well as an excellent stability has been utilized to a variety of electronic devices. Such the lithium ion secondary battery uses a lithium-containing transition metal oxide such as lithium manganate or lithium cobalt oxide as the positive electrode active material and carbon as the negative electrode active material. The charge and discharge are made by utilizing incorporating and eliminating lithium ions into and from the active material.
This lithium ion secondary battery uses a metal oxide with a large specific gravity for the positive electrode. This battery has an insufficient capacity per a unit mass. Accordingly, high capacity batteries were developed using materials of smaller weights. U.S. Pat. No. 4,833,048 and Japanese patent No. 215778 disclose batteries using organic compounds having a disulfide bond. The battery utilizes an oxidation and reduction reaction as an electrochemical reaction with generation of disulfide bonds and dissociation of the bonds. This battery comprises the electrode materials which consist mainly of elements of small specific gravity such as sulfur and carbon. This is effective to the battery with the high energy density and the large capacity. It is, however, disadvantageous that an efficiency of re-forming the bond from once dissociated bond and a diffusion of the active material into the electrolytic solution, whereby cyclic charge and discharge processes reduce the capacity.
Another battery was proposed which uses a conductive polymer as an organic compound for the electrode material. This battery utilizes doping and dedoping reactions of electrolytic ions to be doped into and dedoped from the conductive polymer. The doping reaction is a reaction of stabilizing an exciton with a paired ion, wherein the exciton is a charged soliton or a polaron which is generated through oxidation and reduction of the conductive polymer. The dedoping reaction opposites to the doping reaction. The dedoping reaction is a reaction of electrochemically oxidizing or reducing an exciton stabilized with the pared ion. U.S. Pat. No. 4,442,187 discloses a battery using such the conductive polymer for the positive or negative electrode. The secondary battery comprises elements with a lower specific gravity such as carbon and nitrogen. The secondary battery thus has been expected to be developed as a large-capacity secondary battery. In the conductive polymer, excitons generated by oxidation or reduction are delocalized over a wide region of π-electron conjugated system and interacted with each other. This limits a concentration of excitons generated, and therefore, limits the capacity of the battery. Thus, the secondary battery using the conductive polymer as the electrode material is effective to reduction in weight of the battery but is insufficient in view of obtaining a large capacity.
As described above, there have been various proposals for the secondary battery which does not use any transition-metal containing active material, in order to achieve the large-capacity secondary battery. There had not yet been realized any stable secondary battery with the high energy density and the large capacity.
As described above, the lithium-ion secondary battery using the transition metal oxide for the positive electrode uses elements of large specific gravity, for which reason it had been difficult, in principle, to prepare such a secondary battery with a larger capacity than the existent battery.
Accordingly, it is an objective of the present invention to provide a novel secondary battery being highly stable in charge-discharge cycle processes and having a higher energy density and a larger capacity.